that in some MLS services like NJMLS, listings are classified in several categories as residential (detached single family houses), 2-4 family houses, condo and co-ops, land, commercial, etc. A house can be listed in any of those categories. For example, a house can be listed in both of residential and land, to increase its chances of exposure. Often, especially under current market when a house can not be sold for the price the owner expects, the owner can list the house for sale and for rent at the same time.

All those ML#'s of an identical house (address) can be grouped and picked up by a function of MLS system, called "history" of a property. Sometimes, the owner and/or the listing agent can hide part of the history of a property by some tricks.